The PA sector controller's attention was diverted to another aircraft before completing the initial conflict detection sequence for BAW284. After the initial scan for conflicts was interrupted, the PA sector controller likely formed an expectation that there were no conflicts between BAW284 and KAL231. The existence of this belief is demonstrated by his engagement in non-control transmissions, by the time spent re-entering preferences on the radar display, and by not employing radar situational display functions to check for a conflict between the two aircraft. There was no automatic conflict alert system and, because the PA sector controller was working alone, there was no human redundancy to alert him to the developing conflict. Checking for conflicts is a routine task for controllers; the number of steps in the process and the cognitive load increases with traffic density and complexity. Although traffic density in the sector was light to moderate, various factors increased the cognitive load imposed on the controller. The practice of placing all flight progress strips under one header required the controller to review all 12flight progress strips under the single header in order to identify potential conflict. The controller had estimates for KAL231 over Saskatoon and for BAW284 over the YOUNG intersection, some 63nm east of Saskatoon. Because the controller had not identified that the YOUNG intersection was a common estimate point for the two occurrence aircraft, when he received the YOUNG estimate for BAW284, he did not calculate a YOUNG estimate for KAL231. As a result, there was no conflict warning annotation placed on the flight progress strips of the two aircraft. The controller did not complete the manual task of conflict detection and did not become aware of the conflict between BAW284 and KAL231 until the aircraft were 14.5miles apart, on intersecting tracks, and at the same altitude. The recent implementation of RVSM airspace in the PA sector also contributed to the number of steps and cognitive complexity of the conflict prediction sequence. Although the RVSM airspace was not directly involved in this occurrence, its management requires additional operations by the controller and therefore increases the probability of omission errors. The PA sector controller did not use clear and imperative control instructions to emphasize the urgency of the situation, nor did he issue traffic information to either of the aircraft involved; this likely contributed to the 23second delay before KAL231 began to descend.Analysis The PA sector controller's attention was diverted to another aircraft before completing the initial conflict detection sequence for BAW284. After the initial scan for conflicts was interrupted, the PA sector controller likely formed an expectation that there were no conflicts between BAW284 and KAL231. The existence of this belief is demonstrated by his engagement in non-control transmissions, by the time spent re-entering preferences on the radar display, and by not employing radar situational display functions to check for a conflict between the two aircraft. There was no automatic conflict alert system and, because the PA sector controller was working alone, there was no human redundancy to alert him to the developing conflict. Checking for conflicts is a routine task for controllers; the number of steps in the process and the cognitive load increases with traffic density and complexity. Although traffic density in the sector was light to moderate, various factors increased the cognitive load imposed on the controller. The practice of placing all flight progress strips under one header required the controller to review all 12flight progress strips under the single header in order to identify potential conflict. The controller had estimates for KAL231 over Saskatoon and for BAW284 over the YOUNG intersection, some 63nm east of Saskatoon. Because the controller had not identified that the YOUNG intersection was a common estimate point for the two occurrence aircraft, when he received the YOUNG estimate for BAW284, he did not calculate a YOUNG estimate for KAL231. As a result, there was no conflict warning annotation placed on the flight progress strips of the two aircraft. The controller did not complete the manual task of conflict detection and did not become aware of the conflict between BAW284 and KAL231 until the aircraft were 14.5miles apart, on intersecting tracks, and at the same altitude. The recent implementation of RVSM airspace in the PA sector also contributed to the number of steps and cognitive complexity of the conflict prediction sequence. Although the RVSM airspace was not directly involved in this occurrence, its management requires additional operations by the controller and therefore increases the probability of omission errors. The PA sector controller did not use clear and imperative control instructions to emphasize the urgency of the situation, nor did he issue traffic information to either of the aircraft involved; this likely contributed to the 23second delay before KAL231 began to descend. The Prince Albert (PA) sector controller did not monitor the flight progress strips in sufficient detail to determine that a conflict would occur between two aircraft. As a consequence, there was no planned separation between Korean Airlines Boeing747-200 (KAL231) and British Airways Boeing747-400 (BAW284). The PA sector controller did not adequately use the conflict prediction tools on the radar situational display. As a consequence, detection of the developing conflict and air traffic control intervention to prevent a conflict from occurring was delayed.Findings as to Causes and Contributing Factors The Prince Albert (PA) sector controller did not monitor the flight progress strips in sufficient detail to determine that a conflict would occur between two aircraft. As a consequence, there was no planned separation between Korean Airlines Boeing747-200 (KAL231) and British Airways Boeing747-400 (BAW284). The PA sector controller did not adequately use the conflict prediction tools on the radar situational display. As a consequence, detection of the developing conflict and air traffic control intervention to prevent a conflict from occurring was delayed. Clear and imperative control instructions were not used by the PA sector controller to emphasize the urgency of the heading and altitude change instructions to the aircrew, nor was traffic information passed. As a result, the situational awareness of the aircrew may have been degraded and the desired reaction to the controller's instructions delayed. The reduced use of fix designators as flight progress board headers could require the controller to review more flight progress strips in order to detect potential conflicts and may make it more difficult to detect conflicts by reference to the flight data board. Automatic conflict detection software was not installed in the Winnipeg area control centre (ACC).Findings as to Risk Clear and imperative control instructions were not used by the PA sector controller to emphasize the urgency of the heading and altitude change instructions to the aircrew, nor was traffic information passed. As a result, the situational awareness of the aircrew may have been degraded and the desired reaction to the controller's instructions delayed. The reduced use of fix designators as flight progress board headers could require the controller to review more flight progress strips in order to detect potential conflicts and may make it more difficult to detect conflicts by reference to the flight data board. Automatic conflict detection software was not installed in the Winnipeg area control centre (ACC). Conflict alert functionality is now operational in high-level airspace controlled by Moncton, Winnipeg, Gander, and Edmonton ACCs. Because of software issues not related to conflict alert, Toronto, Montreal, and Vancouver have not yet implemented conflict alert. These software issues were resolved in December. The installation of the software has taken place at all three units, paving the way for conflict alert implementation. It is anticipated that controller conflict alert training will commence shortly in Toronto, with implementation in high-level airspace of the North Enroute speciality to follow. Conflict alert coverage will be expanded to other high-level sectors in Toronto as controller training progresses. Firm dates have not yet been set for implementation in Montreal and Vancouver; however, it is expected that the process will move quickly once controller training is underway. The Edmonton trials in low-level airspace have demonstrated that the current conflict alert functionality is suitable for use at and above 14000feet with the exception of terminal control airspace. As a result, implementation planning for low-level deployment will get underway in the near future. Nav Canada indicated that they will be undertaking a number of initiatives to ensure controllers react appropriately, in a timely manner, and with the correct information to aircrew to minimize the risk of collision potential in a loss-of-separation occurrence. These initiatives include the following: reviewing the current safety alert phraseology as published in the Air Traffic Control Manual of Operations (ATC MANOPS) with a view to developing, if required, additional phraseology for use by controllers in a loss of separation situation; inclusion of the concept of clear and imperative control instructions into basic and refresher training, including specific controller action in the event of a loss-of-separation; and publication of an ATS Bulletin that will highlight the importance of correct and timely action by controllers to resolve a conflict situation with the use of clear and imperative instructions that includes both corrective action and traffic information to all involved aircraft.Safety Action Conflict alert functionality is now operational in high-level airspace controlled by Moncton, Winnipeg, Gander, and Edmonton ACCs. Because of software issues not related to conflict alert, Toronto, Montreal, and Vancouver have not yet implemented conflict alert. These software issues were resolved in December. The installation of the software has taken place at all three units, paving the way for conflict alert implementation. It is anticipated that controller conflict alert training will commence shortly in Toronto, with implementation in high-level airspace of the North Enroute speciality to follow. Conflict alert coverage will be expanded to other high-level sectors in Toronto as controller training progresses. Firm dates have not yet been set for implementation in Montreal and Vancouver; however, it is expected that the process will move quickly once controller training is underway. The Edmonton trials in low-level airspace have demonstrated that the current conflict alert functionality is suitable for use at and above 14000feet with the exception of terminal control airspace. As a result, implementation planning for low-level deployment will get underway in the near future. Nav Canada indicated that they will be undertaking a number of initiatives to ensure controllers react appropriately, in a timely manner, and with the correct information to aircrew to minimize the risk of collision potential in a loss-of-separation occurrence. These initiatives include the following: reviewing the current safety alert phraseology as published in the Air Traffic Control Manual of Operations (ATC MANOPS) with a view to developing, if required, additional phraseology for use by controllers in a loss of separation situation; inclusion of the concept of clear and imperative control instructions into basic and refresher training, including specific controller action in the event of a loss-of-separation; and publication of an ATS Bulletin that will highlight the importance of correct and timely action by controllers to resolve a conflict situation with the use of clear and imperative instructions that includes both corrective action and traffic information to all involved aircraft.